1. Field of the Invention
The present invention relates to transformers; and more particularly, to a dry-type power distribution transformer having a wound amorphous metal core and a generally rectangular resin encapsulated coil.
2. Description of the Prior Art
Conventional dry-type power distribution transformers have a round or toroidal open wound coil and a silicon steel or amorphous metal core of the wound or stacked variety. The transformer core typically has a rectangular shape defining a rectangular window within which the coil is located. Frequently, the toroidal shape of the coil creates a mismatch between the core and coil insofar as the core window is concerned, i.e. the shape of the rectangular window does not match the shape of the section of the coil that is located therein. This mismatch between the core and coil causes the size and cost of the transformer to be significantly larger than would be required if the transformer had more closely matched core and coil shapes.
Wound cores used in power distribution transformers, whether silicon steel or amorphous metal, are rectangular in cross-section and do not conform to the round shape of the coil. Stacked silicon steel transformer cores, on the other hand, may have a cruciform cross-section that can approximately match the coil""s toroidal shape. Due to the high expense of casting or cutting an amorphous metal strip to a variety of widths, it is impractical to form a stacked amorphous metal core with a cruciform cross-section. For these reasons, in manufacture of dry-type power distribution transformers having amorphous metal cores, whether wound or stacked, the cross-sectional shape of the core (i.e. rectangular) and the shape of the coil (i.e. round) do not match. Usage of coil material is uneconomical, and transformer sizes are too large.
Power distribution transformers may be installed in a variety of locations and subject to extreme environmental conditions such as, for example, particulate matter (dust, dirt, etc.), moisture, caustic substances, and the like, which adversely effect the life span and performance of the transformer. Open wound coils provide no protection against the effects of such the harsh environments.
The present invention provides a dry-type power distribution transformer having a wound amorphous metal core and a generally rectangular, resin encapsulated coil. The core has a generally rectangular cross-sectional shape that closely matches the generally rectangular shape of the resin encapsulated coil. By matching the shape of the coil to that of the core""s cross-section, there is provided a dry-type amorphous metal power distribution transformer that is less expensive to manufacture, less resistive and less lossy, in that less coil material is needed to wind the coil, and more compact than transformers having generally round or circular coils.
Generally stated, the dry-type dry-power distribution transformer includes a resin encapsulated generally rectangular coil having a substantially straight section and an amorphous metal core having a generally rectangular core window defined therein. The coil and the core are sized and shaped such that the shape of the substantially straight section of the coil substantially conforms to the shape of the core window. When the coil and core are assembled to form a power distribution transformer, the substantially straight section of said coil is located within the core window. The resin encapsulation protects the coil against harsh environmental conditions, protects the insulation system of the coil, improves the coil strength under short-circuit conditions, and improves the coil""s cooling characteristics by providing a smooth, uniform surface about the coil""s exterior over which air (either forced or convective) may smoothly and easily pass.
Advantageously, the dry-type power distribution transformer of the invention is durable and robust. Coil and core materials are utilized in a highly economical manner that significantly decrease manufacturing cost and transformer size. These features are especially desirable in power distribution transformers where size, cost, and performance govern market acceptance.